During the process of mask write or direct write, several factors contribute to induce errors and prevent the achievement of the expected resolution. Some of these factors are the electron scattering (forward and backward), resist diffusion, resist thickness, etching, flare, fogging, metrology, etc. In order to improve the resolution and reduce the impact of these phenomena, there are several strategies of proximity effect correction (PEC), fogging effect correction (FEC), etching compensation, among others. The strategies are based on a prediction of the impact of each effect of a correction of these by means of dose and/or geometry compensation. Therefore, the quality of the correction depends upon the quality of the models used to predict the phenomena, said models being different from one manufacturing process to another. High precision of the model and the corrections can certainly be obtained, but at a high computation cost.
A problem is that, in any production flow, it is necessary to change the process from time to time. This may come from the purchase of new equipment, new resists, etc. In many cases maintaining identical behavior from the previous flow is desirable. In the prior art, this is achieved by tuning the process conditions. The physical process parameters (etch bias, power, resist thickness, bake, etc . . . ) are changed which is time consuming and quite costly.
Solutions for alleviating this burden have been found in the context of optical proximity effect correction (OPC). Some of these solutions are disclosed by U.S. Pat. Nos. 6,033,814 and 6,463,403. The basic idea of these methods of the prior art is to calibrate the two distinct models, one for the original process and the second for the new process, the output of which have to be matched to those of the original process. Once the two calibrations have been performed, it is necessary to alter the target of the original process into those of the new process using the two calibrated models. Several calculation procedures (two calibrations, one simulation and one correction) have to be run, which is still quite burdensome and computation heavy.